Pt-Al-Hf/Zr coating and method

ABSTRACT

A Pt—Al—Hf/Zr aluminide coating that can be used as a bond coat for TBC and improve TBC spallation life in service at elevated temperatures is provided. The aluminide coating can include a metastable ternary or higher X—Pt/Pd—Ni phase where the phase and other elements in the alloy system are present in a NiAl β phase of the coating. The metastable phase can be present and observable in the as-deposited condition of the bond coating; e.g. in an as-CVD deposited condition of the bond coating.

This application claims benefits and priority of U.S. provisionalapplication Ser. No. 61/216,649 filed May 20, 2009, the entiredisclosure of which is incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to Pt—Al—Hf/Zr aluminide coatings for gasturbine engine blades and components and to a method of introducingalloying elements to a surface region of an alloy.

BACKGROUND OF THE INVENTION

Increased turbine engine performance has been achieved through theimprovements to turbine alloys, cooling scheme, and coatings. The mostimprovement from coatings has been through the addition of thermalbarrier coatings (TBC) to cooled turbine components. For turbine blades,the most effective TBC has been applied by Electron Beam Physical VaporDeposition (PVD). Prior art includes NiCoCrAIY, aluminide andplatinum-aluminide bond coats. Evolutionary improvements to these bondcoats has been realized in terms of optimal processing to produceimproved surface finish or clean processing to reduce the significanteffect of contaminates such as S (sulfur). However, turbine designersare not making full use of TBCs because their predicted life does notmeet the component design life at higher turbine temperature or TBC lifeat existing temperatures are not reliable. Consequently a need for morereliable and longer life TBCs exists.

Addition of Hf to alloys is relatively easy and has shown a significantimpact on TBC spallation life when high Hf alloys [higher than singlecrystal alloys (SXL) specification or directional solidification (DS)alloys with high Hf for improved castability] are coated with currentoutward type Pt—Al aluminide bond coats. SXL alloys have shown 3× to 5×(3 times to 5 times) life improvement while DS MarM247 has been reportedto have 10× life improvement relative to baseline SXL TBC life. For SXL,the high Hf additions impacted SXL alloy microstructure and mechanicalproperties negatively.

SUMMARY OF THE INVENTION

The present invention provides a Pt—Al—X aluminide coating (X is Hfand/or Zr) that can be used beneath a TBC and improve TBC spallationlife in service at elevated temperatures. In an embodiment of theinvention, the Pt—Al—X aluminide coating includes a metastable(transitional) X—Pt/Pd—Ni phase where X is Hf and/or Zr; Pt/Pd means Ptor Pd or both are present in the phase; and where the Ni is presentalone or with other alloying elements, in a β (Ni, Pt)Al outer phase ofthe coating. For brevity the ternary or higher X—Pt/Pd—Ni phase will betermed “μ phase”. The metastable μ phase is present and observable inthe early formation stages of coating development. The μ phase can beobserved in as-deposited condition of the coating; e.g. in an as-CVDdeposited condition of the coating, depending on parameters employed.

In an illustrative embodiment of the invention, a Pt—Al—Hf aluminidebond coating comprises a Pt concentration of about 18 atomic % across acoating thickness region straddling the Hf₂Pt₃Ni_(x) μ phase from oneside to the other. The bond coating has an Al concentration of about 31to about 40 atomic %, such as about 35 to about 40 atomic % in certainembodiments, at the same thickness region straddling the Hf₂Pt₃Ni_(x) μphase from one side to the other. The bond coating has an Hfconcentration of about 0.25 to about 1.0 atomic % across the samethickness region staddling the Hf₂Pt₃Ni_(x) μ phase from one side to theother. The overall bond coating thickness is in the range of about 25 toabout 45 microns, typically about 30 to about 40 microns.

The present invention provides a Pt—Al—X bond coating where X is Hfand/or Zr that can be used beneath a TBC and improve TBC spallation lifein service at elevated temperatures. In an embodiment of the invention,the Pt—Al—X aluminide bond coating includes an outer coating surfacewhere the Pt content is about 2 to about 16 atomic %, such as about 10to about 16 atomic % in certain embodiments, and where the Al content isabout 31 to about 40 atomic %, such as about 35 to about 40 atomic % incertain embodiments, and has an overall coating thickness of about 25 toabout 45 microns, such as typically about 30 to about 40 microns wherethe overall coating thickness includes the diffusion zone and outeradditive region. This embodiment may not have the above μ phase presentin the coating microstructure in the event the coating is subjected toaluminizing times/temperatures or subsequent thermal exposures causingthe metastable phase to dissolve.

The present invention also provides a method comprising introducing anintermediate element (e.g. Pt and/or Pd) on or in a surface region of analloy substrate having a low solubility for another alloying element(e.g. Hf and/or Zr) followed by introducing said another alloyingelement in the intermediate element (e.g. Pt and/or Pd) under depositionconditions to form a surface region of the substrate that is enriched insaid intermediate element and said another element.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1( a) and 1(b) are Pd—Hf and Pt—Zr phase diagrams, respectively.

FIG. 2 is partial phase diagram information of the Hf—Pt system.

FIG. 3( a) is an SEM backscattered image of CVD Hf on Pt plated Ni basesuperalloy.

FIG. 3( b) shows the composition profile of CVD Hf on Pt plated Ni basesuperalloy.

FIG. 4( a) is an SEM backscattered image of CVD Hf plus Al on Pt platedNi base superalloy and a corresponding composition profile of the coatedsurface region.

FIG. 4( b) shows the composition profile of CVD Hf and Pt only showing20% to 30% Hf to Pt ratio.

FIG. 5 shows results from samples of experiment 3 showing the formationof the μ phase with Pt plated sample and no μ phase without Pt plating.

FIG. 6 is an SEM image of a sample of experiment 4 with higher AlCl₃than experiment 3.

FIG. 7 contains SEM images of samples of experiments 3 and 4 before(as-coated) and after heat treatment at 2050 degrees F. for 2 hours invacuum.

FIG. 8 is an SEM image of a sample of experiment 5 showing no evidenceof the μ phase.

FIG. 9 shows spot analyses of sample of experiment 3 with substantial Hfin (Ni,Pt)Al β phase.

FIG. 10 is a Wellbull plot of baseline commercial outward type Pt—Alcoating (MDC-150L) and experiment 6 variants.

FIG. 11 is a bar graph showing spallation life in cyclic oxidationtesting (at 1135 C) of TBC samples having bond coats made pursuant to amethod embodiment using different surface amounts of a Pt layerelectroplated on the samples, No Pt layer, 2 mg/cm² Pt layer, a 4 mg/cm²Pt layer, a 6 mg/cm² Pt layer, and a 8 mg/cm² Pt layer before bondcoating aluminization and hafnization. The samples are compared tosimilar samples that were made using 10 mg/cm² Pt layer electroplated onthe samples before bond coating aluminization and hafnization. Thesamples also are compared to baseline TBC-coated MDC-150L samples havinga 10 mg/cm² Pt layer with standard production aluminizing time and thusis representative of a commercial production coating.

DETAILED DESCRIPTION OF THE INVENTION

For purposes of illustration, the Pt—Al—X coatings where X is Hf and/orZr will be described with respect to chemical vapor deposition (CVD)aluminide diffusion coatings where changes or modifications toconventional CVD coating parameters (U.S. Pat. No. 5,788,823) employedto form outwardly grown aluminide diffusion coatings were made asfollows. The first and second changes are interelated and involve makingthe aluminide bond coating thinner and leaner in Al content. Forexample, the coating thickness can be about 30 to about 40 microns wherethe coating thickness includes the coating affected zone, diffusion zoneand the additive region. In Al lean NiAl, the Ni diffuses about 3-5times faster than the Al. This is the basis for the outward typealuminizing process. This phenomenon continues with additional time attemperature after the coating process is complete. In either case, thehigher flux of Ni diffusing outward causes the NiAl to swell andgenerates a diffusion related strain that contributes to the rumplingphenomenon observed on many aluminide coatings. (The biggest straincontribution to rumpling is from the coefficient of thermal expansionmis-match between the γ/γ′ alloy and the β NiAl. But the swellingphenomenon also contributes.) The higher the Al content, the more Ni isneeded from the substrate to reach the steady state Al content of 30-32atomic % and the more swelling of the NiAl. A thinner and leaner Alcontent bond coating will require less Ni diffusion from the alloyduring formation of the coating and during high temperature serviceexposure. Starting with a thinner, lower Al content coating according tothe invention, will allow the coating system to reach 30-32% Alconcentration (the steady state Al content with gamma prime (γ′)) withless Ni transport and less strain to contribute to the rumplingphenomenon that leads to early TBC spallation.

The third change is a higher surface Pt content in the bond coating ofthe invention. Again, coating time can alter this. The Pt is plated ontothe alloy substrate surface prior to aluminization as described in U.S.Pat. No. 5,788,823. Pt is substitutional with Ni in the γ, γ′ and βphases of the Ni—Al system. The Pt distribution in commercial productionMDC-150L coating is bell shaped with about ½ of the Pt diffusing with Nito form the additive layer of the coating and about ½ diffusing into thediffusion zone toward the alloy.

When plated with 10 mg/cm² Pt, commercial production coating timesproduce a coating outer surface Pt content in the range of 4-8 atomic %.By coating for short times (e.g. 540 minutes or less) pursuant to theinvention, the thinner coating of the invention results in higher Ptcontent at the outer surface of the bond coating. For best TBCspallation results (i.e. prolongation of spallation life of TBC), the Ptcontent at the outer surface of the bond coating of the invention is inthe range of about 10 to about 16 atomic %, which is higher due to lesstime (e.g. 210 minutes or less coating time) for Pt to be diluted by Nidiffusion from the substrate. Additionally, more Pt content can beprovided at the outer surface if desired by plating a greater amount ofPt on the substrate before CVD aluminizing.

Lastly, co-deposition or sequential deposition of Hf (and/or Zr) withthe Al to form the coating allows for Hf (and/or Zr) to becomeincorporated into the β (Ni,Pt)Al outer coating phase. Variousexplanations of the beneficial effects of reactive elements (Hf, Y, La,Ce, Er) on Ni based material oxidation have been reported in addition tothe effect Hf has on TBC spallation life. But the addition to β(Ni,Pt)Al phase at significant levels is also difficult to achieve in aCVD, Above the Pack, or a pack coating environment. Consequently, anembodiment of this invention is a modified CVD process that producessubstantial Hf (and/or Zr) incorporation into the β (Ni,Pt)Al outercoating phase via the formation of an Hf₂Pt₃Ni_(x) metastable(transition) μ phase. In this case Ni_(x) is nickel plus possible otherelements in the alloy system to provide ternary, quaternary or higheralloys present in the β (Ni,Pt)Al phase. For example, for Ni_(x), x canbe 5 when only Ni is present and is less than 5 when the metastablephase includes other alloying elements present in the alloy system inthe β (Ni,Pt)Al coating phase (e.g. Ni_(5-x), where x is/are otheralloying elements in atomic % present in the phase). When Pd plating isused in lieu of Pt plating, another embodiment provides a modified CVDprocess that produces substantial Hf (and/or Zr) incorporation into theβ (Ni,Pd)Al coating phase via the formation of an HfPdNi_(x) metastableternary or higher μ phase where x can be 4 when only Ni is present andis less than 4 when the ternary or higher phase includes other alloyingelements present in the alloy system in the β (Ni,Pd)Al coating phase(e.g. Ni_(4-y) where y is/are other alloying elements in atomic %present in the phase).

One embodiment of the Pt—Al—X bond coats pursuant to the invention areunique in that the bond coat includes an outer coating surface where thePt content is about 2 to about 16 atomic %, preferably about 10 to about16 atomic %, and where the Al content is about 31 to about 40 atomic %,preferably about 35 to about 40 atomic % and has a coating overallthickness of about 25 to about 45 microns, typically about 30 to about40 microns, where the coating overall thickness includes the coatingaffected zone, diffusion zone and additive β (Ni,Pt)Al region. Thisembodiment may not have the above μ phase present in the coatingmicrostructure in the event the coating is subjected to subsequent thelonger alumizing cycles, e.g. greater than 120 minutes, or postaluminizing thermal exposures causing the metastable phase to dissolve.

Another embodiment of the Pt—Al—X bond coats pursuant to the inventionis unique in that the bond coat includes the μ phase in the mid-regionof the coating (e.g. within the middle 40 to 60% of the as-depositedcoating thickness) that is thought to be the position of the Pt platingprior to CVD aluminizing/hafnizing. The presence of the Pt is criticalfor Hf/Zr uptake from the CVD coating gas environment and the ability ofthe β (Ni,Pt)Al phase to hold significant levels of Hf and/or Zr insolid solution. The bond coat pursuant to the invention is capable ofincreasing the TBC spallation life at least 2× (two times) andpotentially 3× longer than the commercial production MDC-150L coating(see U.S. Pat. No. 5,788,823). This invention can be practiced using thesame basic processing equipment as the commercial production MDC-150Lcoating (U.S. Pat. No. 6,793,966 without gas inlet preheater 52) forpurposes of illustration and not limitation. Practice of a methodembodiment of the invention that involves depositing the Hf before theAl to charge the Pt-rich surface with Hf before Al deposition mayimprove uniformity of Hf deposition and allow use of other coating gasdistribution conduits in practice of the invention. Moreover, anothermethod embodiment of the invention envisions using a CVD Hf coating gasgenerator and setting of the coat temperature below the above-the-packactivator reaction temperature to charge the Pt rich surface with Hf,and then raising the coat temperature to above the activator reactiontemperature to start aluminizing.

Examination of a series of phase diagrams provides insight into theconcept of this invention. FIGS. 1( a) and 1(b) show published phasediagrams of the Pd—Hf and Pt—Zr binary alloy systems {Ref: Binary AlloyPhase Diagram 2^(nd) Edition, ASM International, 1990}. FIG. 2 showspublished information of the Pt—Hf binary alloy system. By virtue oftheir location on the Periodic Table of Elements, Pd is above Pt and Zris above Hf in their respective columns, these respective element pairshave similar properties. FIG. 1( a) shows that at 1080 C (degrees C.),Pd can hold more than 20 at. % of Hf in solid solution. Similarly, FIG.1( b) shows that Pt can hold more than 20 at. % Zr in solid solution.Limited data on Pt—Hf suggested that Pt could hold up to 10 at. % insolid solution with the existence of an HfPt₄ phase. The FIG. 1 diagramsdo not show an HfPd₄ or HfZr₄ phase. Consequently there is not completeagreement between the phase stability information as to the maximumsolid solution solubility of Hf in Pt. Nonetheless, the data suggestthat there is at least 10 at. % solid solution solubility which is morethan enough to provide Hf/Zr doping of the bond coat surface inpreparation for bond coat formation and TBC application. Hf doping tothe 0.05% to 1% in (Ni,Pt)Al bond coats can be sufficient to improve TBCspallation life.

The invention uses the high Hf/Zr solubility in Pt to charge the alloysurface (substrate) with Hf/Zr. By Pt plating the Ni based alloysubstrate, the substrate surface is very rich in Pt and provides theopportunity for Hf/Zr to be introduced into the Pt rich surface at highdopant levels. To prove this point, a Chemical Vapor Depositionexperiment was conducted that utilized only HfCl₄ coating gas.

The experiment applied 10 mg/cm² Pt (U.S. Pat. No. 5,788,823) to thesurface of a commercially available single crystal Ni-based superalloy(CMSX-4®) 1-inch diameter×0.125 inch thick coupons. The coupons weresuspended in a CVD reactor (similar to that of U.S. Pat. No. 6,793,966without gas inlet preheater 52). The CVD reactor was thermally ramped to1080 C under a gas mixture of H₂/12.7 volume % Ar at 200 ton. During thethermal ramp, the Pt plate and the Ni superalloy begin to interdiffuse.Once the reactor is at 1080 C, HCl gas is fed into the Hf generator(U.S. Pat. Nos. 6,291,014; 6,793,966; and 6,689,422) to create a coatinggas mixture of H₂/12.6 volume % Ar/0.14 volume % HfCl₄ in the coatingretort. The Hf deposition portion of the coating cycle was held constantfor 25 minutes. Then the retort was cooled and the samples removed forexamination.

FIG. 3 a shows a scanning electron microscope back scatter image andFIG. 3 b shows the composition profile of the resultant coating. Theformation of a high atomic number rich layer is clear by the strongbrightness of the near surface. The composition profile, FIG. 3( b)confirms that the surface is enriched in Hf and the Hf₂Pt₃Ni_(x) μ phaseis present prior to any aluminization processing. In this case Ni_(x) isnickel plus possible other substrate elements. In this case, othersubstrate elements in the μ phase are Co, Ta, Cr, and Al. When combined,they comprised about 6.5 atomic % of the phase.

A second experiment was performed using the same process as describedabove except the Hf only portion was increased to 45 minutes and theHfCl₄ was increased to 0.16 volume % and the Ar to 15.0 volume % andalso the AlCl₃ portion was added after the 45 minutes. The combinedHfCl₄ and AlCl₃ gas mixture flowed for 165 more minutes for a totalcoating cycle of 210 minutes. The combined coating gas mixture comprisedH₂/13.6 volume % Ar/0.15 volume % HfCl₄, and 0.8 volume % AlCl₃. FIGS. 4a and 4 b show the coating and Hf and Pt composition profile made fromthis process. With the additional formation of the additive layer of theoutward type diffusion aluminide processing, the β (Ni,Pt)Al coatingphase has formed over the μ phase. Ni and Pt must be able to transportthrough the μ phase and react with the AlCl₃ to form the β phase. Alsothe μ phase has changed shape. The irregular outer surface of the μphase (adjacent the Ni plating) in FIG. 3 a is smooth in FIG. 4 a. Thesmooth inner surface of μ phase in FIG. 3 a is irregular in FIG. 4 a.The continuous μ phase in FIG. 3 a has gaps in FIG. 4 a. These changessuggest that Ni, Pt, and Hf from the FIG. 3 a μ phase are diffusing. Theouter surface is dissolving and becoming smooth as the additive layerforms. The inner surface is growing towards the diffusion zone in anirregular fashion. If the local chemical conditions are correct, the μphase dissolves to form the gaps.

Experiments three and four were performed using the same process asexperiment 2 except the Hf and Al coating gases were activated at thesame time once the retort was at 1080 C and the coating gas was changedto H₂/12.6 vol. % Ar/0.2 vol. % AlCl₃/0.14 vol. % HfCl₄ for experiment 3and H₂/12.6 vol. % Ar/0.4 vol. % AlCl₃/0.14 vol. % HfCl₄ for experiment4. The total coating time remained at 210 minutes for both experiments.In addition to the Pt plated coupons, non-Pt plated coupons were alsoadded to experiment 4 to understand the criticality of Pt at the surfacein such a process. FIGS. 5 and 6 show the coatings resulting from theseprocessing. The Pt plated samples have similar characteristics toexperiment 2 while the non-Pt plated sample has no μ phase.

A general trend is also noted in that, as the AlCl₃ content of thecoating gas is increased, less of the μ phase is observed. In experiment2, initially there is only Hf available and the μ phase is readilyvisible in the microstructure. As Al availability increases inexperiments 3 and 4, it competes with Hf for reaction with the Ptmodified surface and less μ phase is observed.

Remnant samples from experiments 3 and 4 were heat treated at 2050 F(degrees F.) for 2 hours in a vacuum. FIG. 7 illustrates how the initialμ phase is altered by this heat treatment showing that the μ phase ismetastable and will dissolve with time at temperature. The bright μphase of experiment 3 is diminished to a ghost image of a lesser amountof μ phase after heat treatment. The minimal amount of μ phase in theexperiment 4 sample is completely dissolved.

A fifth experiment to show the metastable nature of the μ phase wasconducted using the same parameters as experiment 4 except the AlCl₃ wasincreased to 0.8 vol. % and the coating time was extended to 420minutes. As shown in FIG. 8, the higher coating gas AlCl₃ content andlonger coating time reduce the amount the μ phase to the point it is notdistinguishable.

An objective of the invention is to provide a method to add Hf (and/orZr) to the (Ni,Pt)—Al bond coat. In particular, Hf enrichment of theadditive layer of the bond coat that forms the thermally grown oxide towhich the thermal barrier coating is anchored. Work with ternaryNi—Al—Hf systems suggests that there is very low solubility for Hf inthe Ni—Al β phase. However, the coating formed on a Ni superalloy formswith other elements from the superalloy allowing for subtle solubilitychanges. Additionally, Al lean, β-NiAl is a more defected crystalstructure allowing for higher solubility of other elements. FIG. 9 showsa set of spot analyses of a sample made in experiment 3. The spots aredivided into 3 groups. The outboard spots are in the β (Ni,Pt)Al coatingregions above the μ phase and the inboard spots are in the β (Ni,Pt)Alcoating regions below the μ phase. The Hf content of the inboard andoutboard β (Ni,Pt)Al coating regions ranges between about 0.5 and about1.0 atomic %.

With the above ability to charge up the Pt rich surface with Hf via theμ phase, the ultimate benefit of this invention is to improve thespallation life of the TBC. To demonstrate this, a baseline coatingprocess (MDC-150L) and three versions of experiment 6 produced 156 bondcoated spallation test coupons. The three versions of experiment 6 usedthe same coating cycle parameters of experiment 5 except for coating gastime. Experiment 6A used 120 minutes, 6B used 210 minutes, and 6C used420 minutes, the same as experiment 5. To show the importance of Ptplating for Hf charging, Experiments 6A, 6B, and 6C had 4 coupons withno Pt plating. To minimize test biasing from the TBC depositionprocessing, the coupons were TBC coated in a series of runs with couponsfrom all four bond coat processes in each of the TBC coating cycles. TheTBC (thermal barrier coating) comprising yttria-stabilized zirconia wasapplied following the process described in U.S. Pat. No. 5,716,720.

Table 3 set forth below is a summary of experimental processingparameters for the 6 experiments (exp.).

Cyclic Testing was performed in vertically mounted Lindberg TubeFurnaces with a suspended sample tree that drops the samples into thefurnace for the exposure time and then elevates them to cool to nearroom temperature. The test cycle is 50 minutes in the furnace and 10minutes of cooling. The test temperature is 2075 degrees F. Each TestRig has automated controllers for conducting the testing around theclock. Before the start of the tests and at furnace service times, thefurnace is surveyed to 2075 degrees F.±10 F.

Each test is run for 20 cycles and allowed to cool before resetting thecounter for an additional 20 cycles. During the 4 hour hold period, thesamples are inspected for failure. After 100 cycles, the samples areremoved from the test rigs and held for the 4 hour holding period andinspected for failure. In each case, failure is defined as 20% of theface of the coupon having TBC spallation.

There are 4 Test Rigs with the above description. Each sample tree holds40 coupons. Since only 40 can be tested at once, additional coupons areadded as failed coupons are removed from the test.

FIG. 10 shows results of the TBC spallation testing of the four bondcoats. The graph is a Weibull plot were the y-axis is a Cumulative %Failure following the formula:

Failure=(R−0.3)/(N+0.4)*100

-   -   R=Failure Rank (1, 2, 3, 4, . . . )    -   N=Total Number of Failures

The x-axis is the cyclic spallation cycles at failure for thecorresponding rank of failure.

Each data set has a Characteristic Life, which is the Cumulative %Failure at 63.2%, and a shape parameter, which is the slope of the dataset. For TBC spallation life, extending Characteristic Life and/orincreasing the slope are desirable qualities.

From FIG. 10 and Table 2 set forth below, it is clear that all 3versions of Experiment 6 show a substantial improvement over thecommercial production MDC-150L baseline (901 cycles). The longer timeExperiment 6C showed the least improvement with a characteristic life of2035 cycles while the shorter time Experiments 6A and 6B showedcharacteristic lives of 2643 and 2674 respectively. The slopes of theExperiment 6 versions are not as steep as the MDC-150L baseline with thelonger 6C Experiment having the poorest slope. The effect of bondcoating time on TBC spallation life is perhaps explained by the loss ofHf due to more diffusion of Hf into the superalloy and away from theTBC/TGO interface, although applicant does not wish or intend to bebound by any theory or explanation in this regard. There appears to bean optimal coating time to achieve maximum TBC spallation life.

Table 2 includes data from Experiments 6A, 6B, and 6C where the Ptplating was not applied to a subset of the samples. This data clearlyshows that these samples performed below the baseline MDC-150Lcharacteristic life reinforcing the need for a Pt rich surface todissolve and retain Hf in the bond coat.

The above examples show how manipulation of CVD processing parameterscan affect the concentration and distribution of Hf in the bond coatingsand hence TBC spallation life. The CVD process methodology gives extradegrees of freedom versus pack or above-the-pack coating processingwhere all constituents must be introduced into the coating environmentas the same time. CVD processing allows for control of when and for howlong each gas species is present in the coating environment. The aboveexperiments represent a sampling of these possibilities and do notrestrict the invention to only those mentioned.

Another embodiment of the present invention involves forming the bondcoating as described above yet using a lesser amount of the applied Pt(or Pd) electroplated layer before aluminization. For example, the aboveembodiments of the invention employed an initial Pt electroplated layerhaving 10 mg/cm² Pt on the sample surface. The following examples employvarious lesser amounts of the Pt layer; namely, no Pt, 2 mg/cm² Ptlayer, 4 mg/cm² Pt layer, 6 mg/cm² Pt layer, and 8 mg/cm² Pt. Thesesamples plus the earlier standard of 10 mg/cm² were then aluminizedaccording to Experiment 6B described above to form the bond coat on thePt plated substrate.

Referring to FIG. 11, a bar graph is provided showing spallation life incyclic oxidation testing (1135 C) of TBC samples (as described above)having bond coats made using the different surface amounts of the Ptlayer electroplated on the samples before bond coating(aluminization+hafnization). The samples designated 0 Pt, 2 Pt, 4 Pt, 6Pt and 8 Pt are compared to similar samples designated 10 Pt and 10 PtMDC-150L, The grey bars were bond coated using the Exp. 6B parameters(aluminization +hafnization) while the black bars, baseline MDC-150L,coating was aluminized per the production practice. Note that 3 sampleshad not failed at this point in the testing.

FIG. 11 reveals that as the amount of the Pt electroplated layer on thesample surface is increased from 0 mg/cm² Pt to 10 mg/cm² Pt, thespallation life is substantially improved, on average, as compared toaverage spallation life of the baseline TBC-coated MDC-150L samples.Moreover, FIG. 11 reveals that a lesser amount of the Pt electroplatedlayer can be used and still provide a spallation life that is equivalentor better than the spallation life provided by the TBC-coated MDC-150Lsamples representative of a commercial production coating. Thisembodiment permits a reduction in the amount of Pt (or Pd) used as aresult of the presence of Hf and/or Zr in the coating in effectiveamount to achieve oxidation resistance substantially equivalent to thatof MDC-150L commercial coating. This embodiment with reduced Pt layeramounts can be employed in making of the bond coat and thus achievesubstantial reduction in materials cost to make the bond coat whereinthe bond coat will provide TBC spallation life in cyclic oxidationtesting as good as or better than that of MDC-150L commercial coating.

TABLE 2 Pt Characteristic Bond Coat (gm/cms²) Life Slope MDC-150L 10 90110.2 Exp 6A 10 2643 6.2 ″ 0 455 3.0 Exp. 6B 10 2674 6.5 ″ 0 393 5.1 Exp6C 10 2035 3.0 ″ 0 358 10.2

TABLE 3 Coating Retort Gas Volume Percent Exp. Cycle Time H2 AlCl3 HfCl4Ar 1 2690 25 85 0 0.17 15.2 2 2335 Hf 45 85 0 0.16 14.9 ″ 2335 Al + Hf165 85 0.9 0.15 13.6 3 2209 210 87 0.2 0.14 12.6 4 2229 210 87 0.4 0.1412.6 5 2414 420 86 0.8 0.14 12.6 6A 2399 120 86 0.8 0.14 12.6 6B 2402210 86 0.8 0.14 12.6 6C 2414 420 86 0.8 0.14 12.6

Although the present invention has been described with respect tocertain illustrative embodiments, those skilled in the art willappreciate that modifications and changes can be made therein within thescope of the invention as set forth in the appended claims.

1. An aluminide coating that includes a X—Pt/Pd—Ni phase, wherein thephase comprises X, which is Hf and/or Zr, one or both of Pt/Pd, and Ni,and wherein the X—Pt/Pd—Ni phase is present in a β (Ni,Pt)Al phase ofthe coating.
 2. The coating of claim 1 wherein the X—Pt/Pd—Ni phase ispresent and observable in the as-deposited condition of the coating. 3.The coating of claim 1 wherein the phase is present and observable inas-CVD deposited condition of the bond coating.
 4. The coating of claim1 wherein the phase comprises X₂Pt₃Ni_(x) where x is 5 or less.
 5. Thecoating of claim 1 wherein the phase comprises XPdNi_(x) where x is 4 orless.
 6. The coating of claim 4 having a Pt concentration of about 18atomic % across a coating thickness region straddling the X₂Pt₃Ni_(x)phase from one side to the other.
 7. The coating of claim 6 having an Alconcentration of about 31 to about 40 atomic %. at the same thicknessregion straddling the X₂Pt₃Ni_(x) phase from one side to the other. 8.The coating of claim 7 having an Al concentration of about 35 to about40 atomic % at the same thickness region straddling the X₂Pt₃Ni_(x)phase from one side to the other.
 9. The coating of claim 4 having an Hfconcentration of about 0.25 to about 1.0 atomic % across the samethickness region straddling the Hf₂Pt₃Ni_(x) phase from one side to theother.
 10. The coating of claim 9 wherein the Hf is about 0.5 to about1.0 atomic %.
 11. A Pt—Al—X aluminide coating where X is Hf and/or Zrand including an outer coating surface where the Pt content is about 2to about 16 atomic and where the Al content is about 31 to about 40atomic %, and Hf and/or Zr is/are present, and having a coatingthickness of about 25 to about 45 microns where the overall coatingthickness includes a diffusion zone and an additive region.
 12. Thecoating of claim 11 wherein the overall thickness is about 30 to about40 microns.
 13. The coating of claim 11 wherein the Pt content is about10 to about 16 atomic %.
 14. The coating of claim 11 wherein the Alcontent is about 35 to about 40 atomic %.
 15. The coating of claim 11including 0.25 to 1.0 atomic % Hf and/or Zr near the outer coatingsurface.
 16. The coating of claim 15 wherein the Hf is about 0.5 toabout 1.0 atomic %.
 17. A method comprising introducing an intermediateelement on or in a surface region of an. alloy substrate having a lowsolubility for another alloying element followed by introducing saidanother alloying element in the intermediate element under depositionconditions to form a surface region of the substrate that is enriched insaid intermediate element and said another element.
 18. The method ofclaim 17 wherein the intermediate element comprises Pt or Pd or both.19. The method of claim 17 wherein the Pt is provided in amount of about2 mg/cm² to about 8 mg/cm².
 20. The method of claim 17 wherein the saidanother alloying element comprises Hf or Zr or both.
 21. The method ofclaim 17 wherein chemical vapor deposition conditions are used tointroduce said another alloying element in the intermediate element. 22.A method of making an aluminide coating on a substrate surface region,comprising depositing an intermediate element as a layer on or in thesurface region of the substrate having a low solubility for anotheralloying element, depositing said another alloying element on the layerunder deposition conditions to form a phase on or in the surface region,which phase includes said intermediate element and said another element,and aluminizing the substrate under conditions to form a diffusionaluminide coating.
 23. The method of claim 22 wherein the intermediateelement comprises Pt, Pd or both, as a layer on the surface region. 24.The method of claim 23 wherein the Pt is deposited in amount of about 2mg/cm² to about 8 mg/cm².
 25. The method of claim 22 wherein the saidanother alloying element comprises Hf, Zr, or both.
 26. The method ofclaim 22 wherein said another alloying element is codeposited withaluminum on the surface region.
 27. The method of claim 22 wherein saidanother alloying element is deposited on the surface region followed bydeposition of aluminum alone or concurrently with said another alloyingelement.
 28. The method of claim 22 wherein chemical vapor depositionconditions are used to deposit said another alloying element on thelayer to form said phase.
 29. The method of claim 22 wherein the phasecomprises Pt and/or Pd, Hf and/or Zr, and Ni.
 30. The method of claim 29wherein the phase comprises X₂Pt₃Ni_(x) where x is 5 or less.
 31. Themethod of claim 22 wherein Pt is deposited on the surface region in anamount from about 2 mg/cm² to about 8 mg/cm² Pt.
 32. The method of claim31 wherein Pt is deposited on the surface region in an amount from about4 mg/cm² to about 6 mg/cm² Pt.
 33. The method of claim 22 includingdiscontinuing aluminizing after a time to retain the phase in thecoating microstructure.
 34. The method of claim 22 including continuingaluminizing for a time that the phase disappears from the coatingmicrostructure.
 35. A method of making an aluminide coating on asubstrate surface region, comprising depositing Pt and/or Pd as a layeron a surface region of a substrate, depositing Hf and/or Zr on or in thelayer under conditions to form a phase comprising Pt and/or Pd, Hfand/or Zr, and Ni, and aluminizing by chemical vapor deposition to formthe aluminide coating.
 36. The method of claim 35 wherein Pt isdeposited on the surface region in an amount from about 2 mg/cm² toabout 8 mg/cm² Pt.
 37. The method of claim 36 wherein Pt is deposited onthe surface region in an amount from about 4 mg/cm² to about 6 mg/cm²Pt.
 38. The method of claim 35 including discontinuing aluminizing aftera time to retain the phase in the coating microstructure.
 39. The methodof claim 35 including continuing aluminizing for a time that the phasedisappears from the coating microstructure.